(In reply to a solution
This solution looks good to me, except that I don't think you have explained how to do "parallel creases". I have a method that works, but only if the initial creases form five equal spaces on the long side. In other words, you need to start your process by folding the short side less than a fifth of the way towards the other short side.
I had wondered initially why the puzzle framer specified the rectangle was not square, and it might be because of this nuance.